The development of highly absorbent materials and structures for use in diapers, catamenial products, bandages, and the like, is the subject of substantial commercial interest. Originally, such products relied on various cloth or cotton fibers to provide absorbency. Further progress in the field of absorbent materials and structures came with the development of various air-laid cellulosic pulp batts which, in general, will absorb up to 5-6 times their own weight of aqueous body fluids such as urine. Most recently, the use of absorbent gelling materials, such as the polyacrylates, in combination with cellulosic fibers has substantially increased the absorbent capacity of absorbent articles such as diapers and has allowed the manufacture of the relatively thin diapers which are currently commercially marketed. However, even with these improvements, the search for still better absorbent materials and structures continues.
To the uninitiated, it might seem reasonable to suggest that ordinary sponge materials which, in their broadest aspects, might be considered to be open-celled foams, would be quite useful in absorbent structures and articles. For example, both natural sponges and artificial cellulosic sponges have been used to mop up water and other fluids since time immemorial. However, on closer consideration, it will be appreciated that such sponges are not particularly suitable in high performance body fluid absorbing articles of the type currently envisioned. For example, absorbent articles are, initially, used in the dry state. It is well known that many dry sponge materials are quite stiff (rigid) and harsh feeling to the skin and, therefore, would not be suitable for use in diapers and other incontinence products. Furthermore many common sponge materials can have non-uniform cell sizes and partially or completely closed cells which hinder fluid wicking through and fluid retention by the sponge. Finally, while common sponge materials can imbibe substantial quantities of aqueous fluids, they can also release the imbibed fluids with very little pressure. Accordingly, such sponge materials would be entirely unsuitable for use in situations where the absorbent structure is used under conditions wherein pressure is applied, for example, when a diapered child sits down.
Besides common "sponges," the literature and commercial practice are replete with descriptions of various types of polymeric foams which can imbibe a variety of fluids for a variety of purposes. It is also known to employ certain types of polymeric foam materials as elements of absorbent articles such as diapers and catamenial products. For example, Karami; U.S. Pat. No. 4,029,100, Issued Jun. 14, 1977 discloses a shape-retaining diaper which can employ a foam element in the crotch area of its absorbent pad assembly in order to provide high wet resiliency for the pad assembly.
Certain types of foam materials have also been disclosed as being useful in absorbent articles for the purpose of actually imbibing, wicking and/or retaining aqueous body fluids. For example, Lindquist; U.S. Pat. No. 3,563,243; Issued Feb. 16, 1971 discloses an absorbent pad for diapers and the like wherein the primary absorbent therein is a hydrophilic foam sheet formed from hydrophilic polymers. Such foam sheets are said to be formed by combining poly(oxyethylene) glycols with diisocyanates. Dabi; U.S. Pat. No. 4,554,297; Issued Nov. 19, 1985 discloses body fluid absorbing cellular polymers which can be used in diapers or catamenial products. Such cellular polymers comprise the reaction products of at least one epoxy resin and an amine-terminated poly(alkylene oxide). Garvey et al ; U.S. Pat. No. 4,740,528; Issued Apr. 26, 1988 discloses absorbent compositer structures such as diapers, feminine care products and the like, which contain a sponge absorbent composition made from a certain type of super-wicking, crosslinked polyurethane foam.
Notwithstanding the known uses of various polymeric foam types as elements in absorbent articles for body fluids, there is a continuing need to identify additional absorbent foam materials having an optimized combination of features and characteristics which render such foams especially useful in commercially marketed absorbent products such as diapers. It has now been determined that optimized absorbent foams for body fluids, and especially foams intended for use in diapers and adult incontinence products, should have the following characteristics:
a) Flexibility and preferably recovery from compression, for comfort and performance; PA1 b) Acceptable fluid acquisition rate, in order for the foam to rapidly accept and imbibe gushes of urine or other fluids; PA1 c) Relatively good wicking and fluid distribution characteristics in order for the foam to transport the imbibed urine or other fluid away from the zone wherein the fluid initially impinges onto the foam and into the unused balance of the foam structure, thereby allowing for subsequent gushes of fluid to be accommodated; PA1 d) Relatively high total storage capacity with relatively high fluid capacity under load, i.e., under compressive pressure; and PA1 e) Relatively low density in order for the foam to exhibit suitably high total storage capacity and to comprise a thin soft material. PA1 f) Relatively greater affinity for absorbing body fluids than exhibited by other absorbent article components so that the foam material can drain (partition) fluids from these other components and keep such fluid stored within the foam structure.
It will be appreciated that absorbent foams having the foregoing characteristics would provide the features of fluid acquisition, transport, storage which are required for use in high performance absorbent articles. Optimized foams would, preferably, also be soft to the touch. Of course, absorbent foams intended for use in contact with or in proximity to the skin should cause no damage or irritation to the skin nor expose the user to toxic chemicals. Since they are intended for use in disposable articles such as diapers, such preferred optimized foams should also be relatively inexpensive and easy to manufacture and should be compatible with responsible solid waste disposal systems such as those based on landfills, incineration and/or composting.
It will also be appreciated by the manufacturer of absorbent articles that optimized absorbent foam materials of the type hereinbefore described would represent a substantial advance in the industry. Absorbent articles containing such foams would possess desirable wet integrity, would enable suitable fit through the entire period the article was being worn, would not degrade in shape during use, and would provide desirable skin dryness.
Absorbent articles containing such foam structures would also be easier to manufacture on a commercial scale. For example, diaper product cores could be simply stamped out of continuous foam sheets and could be designed to have considerably greater integrity and uniformity than air-laid absorbent cores. Such foams could furthermore be molded in any desired shape, or even formed into integral, unitary diapers or panty-like structures. Alternatively, such foam materials could be combined, e.g., blended, with other conventional absorbent structure components.
The present invention identifies the parameters which define optimized absorbent foam materials that are especially adapted for use in absorbent articles for body fluids such as urine. The invention herein also provides absorbent foams which overcome a number of the drawbacks of foam materials heretofore used in body fluid absorbing articles.